It is known for the intensity distribution of microwaves which are transmitted through a transmission wall from a chamber into a treatment chamber to be influenced by a special design of the transmission wall. DE 94 05 808 U discloses a plasma processing device in which a plasma is produced in a treatment chamber by means of microwaves that are introduced, for example for surface processing of objects which are introduced into the treatment chamber. In this case, the microwaves are produced in a rectangular hollow waveguide of elongated design, and are output at the side via a waveguide which projects into the hollow waveguide. In this case, the waveguide is designed in the form of a disk and forms a boundary wall for the treatment chamber. In order to introduce the microwave energy uniformly into the treatment chamber, a screen of conductive material is located between the waveguide and the treatment chamber, which screen is designed as a perforated metal sheet, the size of the through-holes increasing as the distance from the hollow waveguide increases, in order in this way to make it possible to compensate for the decrease in the microwave energy as the distance from the hollow waveguide increases.
The use of such a screen as a transmission wall of the treatment chamber leads, however, to a considerable reduction in the microwave energy introduced into the treatment chamber. The introduction of energy into the treatment chamber is thus made uniform at the expense of a considerable reduction in the microwave energy.
It is furthermore known for it to be possible to produce a plasma in a treatment chamber by radio-frequency excitation as well.